Pressure-sensitive adhesives ("psa's") made from the photopolymerization of an alkyl acrylate (e.g., isooctyl acrylate) and a polar copolymerizable monomer (e.g., acrylic acid, N-vinyl pyrrolidone, etc.) are well known in the art; see, for example, U.S. Pat. Nos. 4,181,752; 4,364,972; and 4,243,500. Such acrylic-based psa's exhibit good adherence to high energy (i.e., polar) substrates such as metal and painted steel surfaces, but exhibit limited adhesion to low energy (i.e., nonpolar) substrates such as polyethylene and polypropylene. Additionally, whereas the acrylic-based psa's have good high temperature (e.g., 100.degree. C.) performance properties due to the presence of the polar copolymerizable monomers (which increase the cohesive or internal strength of the adhesive), they also exhibit limited adhesion at low temperatures (e.g., -45.degree. C.).
Pressure-sensitive adhesives based upon polymers of alpha (.alpha.)-olefins are also well known; see, for example, U.S. Pat. Nos. 3,635,755; 3,954,697; 4,178,272; and 4,288,358 as well as EPO No. 416,921. Psa's based upon .alpha.-olefin polymers tend to exhibit good adhesion to low energy substrates, but only moderate adhesion to high energy substrates. Additionally, they have good low, but limited high, temperature performance properties.
As can be seen from the foregoing discussion, acrylic- and .alpha.-olefin-based psa's do not individually exhibit a broad spectrum of desirable adhesive properties. Mere blending together of the two different psa's does not provide an acceptable adhesive because the resulting blend does not produce a psa with a wide spectrum of performance properties either. It was against this background that the development of a psa material which exhibits good adhesion to both low and high energy substrates as well as good high and low temperature performance properties was sought.